linux-kernel - Re: [PATCH 0/7] slub: Fastpath optimization (especially for RT) V1

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Date:	Thu, 18 Dec 2014 23:38:09 +0900
From:	Joonsoo Kim <js1304@...il.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Joonsoo Kim <iamjoonsoo.kim@....com>, akpm@...uxfoundation.org,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Pekka Enberg <penberg@...nel.org>,
	Jesper Dangaard Brouer <brouer@...hat.com>
Subject: Re: [PATCH 0/7] slub: Fastpath optimization (especially for RT) V1

2014-12-18 0:36 GMT+09:00 Christoph Lameter <cl@...ux.com>:
> On Wed, 17 Dec 2014, Joonsoo Kim wrote:
>
>> Ping... and I found another way to remove preempt_disable/enable
>> without complex changes.
>>
>> What we want to ensure is getting tid and kmem_cache_cpu
>> on the same cpu. We can achieve that goal with below condition loop.
>>
>> I ran Jesper's benchmark and saw 3~5% win in a fast-path loop over
>> kmem_cache_alloc+free in CONFIG_PREEMPT.
>>
>> 14.5 ns -> 13.8 ns
>>
>> See following patch.
>
> Good idea. How does this affect the !CONFIG_PREEMPT case?

One more this_cpu_xxx makes fastpath slow if !CONFIG_PREEMPT.
Roughly 3~5%.

We can deal with each cases separately although it looks dirty.

#ifdef CONFIG_PREEMPT
XXX
#else
YYY
#endif

Thanks.
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